Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, and non-open-world, so the safety profile is covered. The description adds meaningful context beyond that: that signature verification is NOT performed and that dates are rendered as absolute ISO timestamps – both are non-obvious behavioral facts.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tight sentences, front-loaded with the core action and followed by the two most decision-relevant caveats (timestamp format, unverified signature). No filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a single-parameter read-only utility with an output schema and full annotation coverage, the description covers purpose, output shape, and the key security caveat. Only explicit routing/usage guidance is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% for the single token parameter, and the schema itself documents the optional Bearer prefix. The description adds no parameter-specific detail beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb (Decode) and resource (a signed JSON Web Token), and enumerates what the agent gets back: header, payload, and registered claims. Since no sibling tool decodes JWTs, this is unambiguously distinguishable.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The 'signature is not checked' caveat implicitly steers the agent away from using this for verification, but there is no explicit when-to-use or alternative named (e.g., where to verify a signature). Usage is only implied.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.